Hydraulic machines such as excavators, dozers, loaders, backhoes, motor graders, and other types of heavy equipment use one or more hydraulic actuators to accomplish a variety of tasks. These actuators are fluidly connected to an engine-driven pump of the machine that provides pressurized fluid to chambers within the actuators. As the pressurized fluid moves into or through the chambers, the pressure of the fluid acts on hydraulic surfaces of the chambers to affect movement of the actuators and a connected work tool.
Swing-type excavation machines, for example hydraulic excavators and front shovels, require significant hydraulic pressure and flow to transfer material from a dig location to a dump location. These machines direct the high-pressure fluid from an engine-driven pump through a swing motor to accelerate a loaded work tool at the start of each swing, and then restrict the flow of fluid exiting the motor at the end of each swing to slow and stop the work tool.
One problem associated with this type of hydraulic arrangement involves efficiency. In particular, the pressurized oil provided by the pump may slowly accelerate the work tool to its steady state swing speed, making the hydraulic system less responsive to the operator swing commands than is desirable to efficiently complete the required tasks. Moreover, the fluid exiting the swing motor at the end of each swing is under a relatively high pressure due to deceleration of the loaded work tool. Unless recovered, energy associated with the high-pressure fluid may be wasted. In addition, restriction of this high-pressure fluid exiting the swing motor at the end of each swing can result in heating of the fluid, which must be accommodated with an increased cooling capacity of the machine.
One attempt to recover swing kinetic energy in a swing-type machine is disclosed in U.S. Pat. No. 8,850,806 to Zhang et al. issued on Oct. 7, 2014 (the '806 patent). The '806 patent discloses a hydraulic control system for a machine that may have a work tool movable through segments of an excavation cycle, a motor configured to swing the work tool during the excavation cycle, at least one accumulator configured to selectively receive fluid discharged from the motor and to discharge fluid to the motor during the excavation cycle, and a controller. The controller may be configured to receive input regarding a current excavation cycle of the work tool, and make a determination based on the input that the current excavation cycle is associated with one of a set of known modes of operation. The controller may be further configured to cause the at least one accumulator to receive fluid by actuating an electro-hydraulic charging valve, and to discharge fluid by actuating an electro-hydraulic discharge valve, during different segments of the excavation cycle based on the determination. The arrangement with two electro-hydraulic valves provides flexibility in design as the performance of the valves is tuned to the particular machine in which the hydraulic control system is implemented. The discharge valve discharges recovered energy in the accumulator directly back to the swing motor during swing acceleration. However, swing acceleration performance can vary based on the pressure within the accumulator at a given time. Moreover, the discharge valve cannot be opened during charging portions of the excavation cycle, so excess kinetic energy may be wasted or lost once the accumulator is fully charged. Therefore, opportunities exist for providing energy recovery systems in swing-type machines that provide more consistent performance in swing acceleration, are more portable between different sizes and types of machines, and are more efficient at capturing kinetic energy.
The swing-type elevation machines (e.g., excavators, front shovels, backhoes, etc.) and other non-swing-type elevation machines (e.g., wheel loaders, bulldozers, telehandlers, etc.) may be used to move heavy loads, such as earth, construction material, and/or debris, and may utilize an implements to move the loads. The implements may be powered by hydraulic systems that similarly use pressurized fluid to actuate a hydraulic actuator to lift the implement. During operation of a lifting machine, the implement with or without a load of material may be raised to an elevated position. As the implement and the load may be relatively heavy, the implement may gain potential energy when raised to the elevated position. As the implement is released from the elevated position, this potential energy may be converted to heat when pressurized hydraulic fluid is forced out of the hydraulic actuator and is throttled across a valve and returned to a tank. The conversion of potential energy into heat may result in an undesired heating of the discharged hydraulic fluid, which may require that the machine possess additional cooling capacity. However, recovering that lost or wasted potential energy for reuse in the hydraulic system may improve the machine's efficiency.
An energy recovery system having integrated boom and swing circuits is disclosed in U.S. Pat. Appl. Publ. No. 2014/0119867 to Wen et al. published on May 1, 2014 (the '867 publication). The '867 publication discloses an energy recovery system that may have a boom circuit with at least a one linear actuator configured to move a work tool, and a boom accumulator configured to selectively collect pressurized fluid from the at least one linear actuator and to discharge pressurized fluid back to the at least one linear actuator. The energy recovery system may also have a swing circuit with a swing motor configured to move the work tool, and a swing accumulator configured to selectively collect pressurized fluid from the swing motor and discharge pressurized fluid back to the swing motor. The energy recovery system may further have a common supply passage extending between the swing and boom circuits to connect discharge passages, and a combiner valve may be disposed within a common supply passage. The combiner valve may be selectively moved to combine the outputs of pumps of the circuits to provide supply fluid for only the swing circuit, for only the boom circuit, or for both the swing and the boom circuits. A common return passage may also extend between the swing and boom circuits, and may connect the return passages of the swing circuit and the boom circuit. In this manner, a makeup accumulator may be filled with fluid from both circuits and, likewise, the makeup accumulator may provide fluid to both circuits. In such systems, the swing circuit and the boom circuit work independently with separate motors and accumulators. The circuits show improved efficiency when integrated as taught by the '867 publication, but may be more difficult to implement in smaller machines due to the package size required for the motors and accumulators. In view of this, opportunities exist for integrating boom and swing circuits in a manner that is portable between the machines in which the energy recovery system may be implemented.